The present invention relates to a tire for use on motor vehicle wheels, of the type comprising: a pair of beads each of which defines an inner circumferential edge of the tire; a pair of sidewalls, each of which is in the form of an annulus and extends in a radial direction away from one of said beads; a tread band of substantially cylindrical conformation the outer peripheral edges of the sidewalls at respective buttress areas, said tread band having a patterned annular surface at its junction with the sidewalls.
It is known that tires presently used in the automotive field have a tread band in the form of a cylindrical surface arranged to contact the roadway, two sidewalls extending in a radial direction from the opposite edges of the tread band and two beads defined at the radial inner end of the respective sidewalls along the inner circumferential edges of the tire. In known tires, the sidewalls have a substantially smooth surface on which different inscriptions such as the brand of the tire-producing company, model, particular technical data and other information, are printed.
The above inscriptions sometimes encounter some readability problems in that the contrast between the inscription surface and background surface, that is the remaining surface of the tire sidewall, is not very strong and in that the incident light on the tire sidewall, except in very favorable lighting conditions, creates two opposed circular sectors which are well-lighted but of very reduced width, whereas all the remaining portion of the sidewall is left in the shade, so that only a small part of said inscriptions is highlighted.
As regards contrast, solutions tending to enhance it have been long since adopted, such as writing the inscriptions in relief with respect to the background, knurling the inscription surface or emphasizing the edges of said inscriptions with respect to the central part thereof. These expedients have only partly solved the problem related to the inscription readability, but without dealing with the aspect connected with the tire sidewall lighting.
It must also be noted that in the tire vulcanization process carried out in a closed mold, it is required that the air that has been trapped between the mold cheek and the tire sidewall should be vented during the mold closure; in order to enable this air escape, the solutions of the known art make it necessary to form a great number of small holes on the mold cheeks which holes not only require frequent and difficult mold cleaning operations, but also give rise to the presence, on the finished workpiece, of hair-like projections consisting of the vulcanization stems created by the elastomeric material which penetrates into the small holes during the vulcanization step. These unaesthetic hair-like projections must be eliminated by carrying out a finishing operation on the vulcanized tire.
In addition to the above, a correct and optimal distribution of these small holes on the mold cheek for air escape purposes would inevitably involve the presence of some small holes on the inscriptions as well or in close proximity thereto: but since the relative hair-like projections would aesthetically impair these inscriptions to a great degree, it is better to form a greater number of small holes, provided that they are far from the inscriptions.
From the U.S. Des. Pat. No. 87,418 a tire for motor vehicles is known which has the sidewalls devoid of informative inscriptions and a rounded-profile tread. Two series of grooves depart from the tread center line of said tire and they symmetrically extend on the opposite sidewalls of the tire up to the bead area.
In this tire the problem related to the sidewall hair-like projections seems to be overcome by renouncing the inscriptions and through a plurality of grooves extending radially from the bead to the buttress and circumferentially distributed on the tire sidewall, which grooves constitute the prolongation of the tread pattern grooves. Since these grooves ensure air escape towards the tread, they make it useless to provide small venting holes on the mold cheeks.
In accordance with the present invention, the Applicant has found that by defining at the tire sidewalls an annular strip having a plurality of circumferentially distributed ribs crossing the annular strip itself, it is possible to affix informative inscriptions on the surface of said strip, the readability of which is greatly improved while at the same time achieving a better luminosity of the whole tire sidewall and important advantages from the production point of view.
In greater detail, the present invention relates to a tire for use on motor vehicle wheels comprising a pair of beads each of which defines an inner circumferential edge of the tire, a pair of sidewalls, each of which is in the form of an annulus and extends in the radial direction and away from one of said beads and a tread band of substantially cylindrical conformation the axially opposite edges of which are joined to the sidewalls at respective buttress areas. On the outer surface of at least one of said sidewalls a surface patterned annular strip is located, the radial extension of which is defined between an inner peripheral edge disposed in the area included between the relative bead and the maximum width circumferential line of the tire, and an outer peripheral edge substantially coincident with the edge of the tread band at the corresponding buttress area. On said annular strip a plurality of ribs are formed which are disposed consecutively in side by side relation, are circumferentially distributed and extend each substantially according to a direction intersecting at least the outer periphery edge of said annular strip.
Advantageously informative inscriptions are formed on the annular strip in a unitary manner.
In accordance with the invention, the annular strip is formed on the corresponding tire sidewall in the form of a surface hollow of predetermined depth, said ribs having a height lower than said depth.
Preferentially, the height of said ribs is not lower than half the depth of said surface hollow.
According to a preferred choice, said informative inscriptions are defined by a plurality of projections emerging from said annular strip according to a height greater than that of said ribs and, preferably, greater than the depth of said surface hollow.
In accordance with a further aspect of the invention, each of said ribs has a trapezoidal-shaped profile and a substantially rectilinear extension.
In greater detail, each of said ribs extends from the inner peripheral edge to the outer peripheral edge according to a given angle of inclination with respect to a radial straight line issuing from the inner peripheral edge at the crossing point with the rib itself, each rib being spaced apart from the adjacent rib according to an arc that on the inner peripheral edge subtends a respective central angle of predetermined opening.
In one embodiment said angle of inclination, identical for wall ribs, is generally included between 60xc2x0 and 90xc2x0 and, preferentially, lower than 85xc2x0. In said embodiment, the arc and the central angle are identical for all pairs of adjacent ribs. In particular the arc has an amplitude included between 0.8 mm and 5 mm whereas the central angle has an opening included between 0.0178xc2x0 and 1.35xc2x0.
According to a second embodiment of the tire of the invention, a plurality of sectors of an annulus having the same angular extension is defined along the circumferential extension of said annular strip, each of them having, along the circumferential extension thereof, a gradual increase of the angle of inclination of the individual ribs, together with a gradual increase of the values of said arc and central angle.
Preferably, the annular strip has two or four of said sectors of an annulus.
In greater detail, in each of said sectors the value of said angle of inclination increases continuously from 0xc2x0 to 90xc2x0 while at the same time the value of said arc increases continuously from 0.8 mm to 5 mm and likewise the value of said central angle increases continuously from 0.0178xc2x0 to 1.35xc2x0.
According to a further embodiment of the invention, the annular strip has a predetermined number of sectors of an annulus having the same annular extension, preferably substantially equal to 180xc2x0, each of said sectors having first and second series of ribs extending from the inner peripheral edge and the outer peripheral edge respectively, each rib of the first series intersecting a corresponding rib of the second series at a respective point of mutual break.
In more detail, each rib of the first series is inclined in the opposite way to that of the corresponding rib of the second series with respect to a radial direction passing through the respective point of mutual break. Preferentially, said points of mutual break are consecutively aligned according to a spiral-shaped line extending from the inner peripheral edge to the outer peripheral edge.
Finally, the number of said ribs present in said annular strip are preferably greater than 200.